Disorders of mineral metabolism have been evaluated with methods extending from epidemiology to cellular biology. Two forms of familial hyperparathyroidism have been characterized in detail. Familial hypocalciuric hypercalcemia is an autosomal dominant trait associated with abnormal interactions with calcium in parathyroid and kidney. Parathyroid cells from a presumed FHH homozygote showed a strikingly decreased sensitivity to secretory suppression by calcium. Familial multiple endocrine neoplasia type 1 is an autosomal dominant trait causing hyperfunction of parathyroids, pancreatic islet, and anterior pituitary. It is associated with gradual but abnormal proliferation of the tissues affected. Plasma from affected persons shows high mitogenic activity upon cultured bovine parathyroid cells.